The LSUHSC New Orleans Emergency Medicine Interest Group Presents The Student Procedure Manual

Radial Artery Puncture for Arterial Blood Gas (ABG)

Indications

• Arterial blood gas sampling to confirm/rule-out hypoxia, CO2 retention, acid-base abnormality, CO poisoning (COHb), nitrate poisoning (MetHb) and to obtain arterial blood for other blood tests such as ammonia level, lactic acid level and etc...

Contraindications (relative)

• Coagulopathy
• Severe atherosclerosis
• Infection/bum/previous surgery or cutdown at site
• Decreased collateral flow

Prerequisites

Allen test: The radial artery is the most common site for ABG sampling. One of the risks of this procedure is thrombosis, which would decrease or block perfusion distally. It is an absolute necessity to ensure that the ulnar artery provides good collateral blood flow to the hand. The Allen test verifies the presence of a patent ulnar artery providing sufficient blood flow to keep the hand perfused in the event of loss of flow from the radial artery.

• Have the patient make a tight fist.
• Using your thumbs, occlude both the radial and ulnar arteries just proximal to the flexor crease of the wrist.
  
• Ask the patient to open his or her hand.
  
• After a few seconds of occlusion, the hand should be pale.
  
• Release pressure on the ulnar artery, while keeping the radial artery occluded.
  
• Color should return to the hand within 6 seconds. (the hand should flush red)
  
• Repeat the test, but release the pressure on the radial artery only.
  
• The time for color to return to the hand should be about the same.
  
• If it takes significantly longer for color to return to the hand when the ulnar artery is released, as compared to the radial artery, collateral circulation to the hand is insufficient and another site for ABG sampling should be chosen.
  
• If color returns quickly after the ulnar artery is released, proceed with the procedure.

Equipment (usually provided in an ABG sampling kit)

• 3-5 ml pre-heparinized syringe (if syringe is not preheparinized, draw 1 ml of heparin solution (1: 1000 or 1000 IU per ml) into the syringe, moving the plunger up and down a few times to coat the barrel of the syringe. Then expel all of the visible heparin through the needle immediately before drawing blood, leaving only a trace of heparin in the needle and in the syringe.)
  
• 25 gauge needle
  
• Alcohol swabs
  
• Iodine-based antiseptic swabs
  
• Gauze pad
  
• Cup or bag of ice
  
• Protective equipment for universal precautions

Procedure

1. Wear latex gloves
   
2. The patient's hand should be supinated and the wrist dorsiflexed slightly, with the forearm resting on a comfortable surface. No tourniquet is used.
   
3. Do an Allen test.
   
4. Palpate the radial artery pulse about 2 cm proximal to the flexor crease of the wrist.
   
5. Prepare the area with an iodine-based antiseptic swab and/or an alcohol swab.
   
6. With your non-dominant hand, use the index and middle fingers to locate and trap the radial artery, maintaining control of it in a lcm (approx.) space between the fingers along the artery.
   
7. Holding the syringe like a pencil with the needle bevel up, enter the skin with the needle angled towards the flow of blood, in the space between the fingers controlling the artery.
   
8. Upon entering the lumen of the artery, blood should flow into the syringe, pushing the plunger back due to the arterial pressure. Allowing the syringe to passively fill in this manner ensures that a venous sample is not being taken. A very slight pull on the plunger may be necessary. If no blood flows into the syringe, withdraw slightly because the needle may have passed through both walls of the vessel. It may be possible to see the blood pulsate into the syringe as it fills, further evidence that the sample is arterial in origin.
   
9. If no blood flows into the syringe, it may be necessary to slowly withdraw partially and redirect the syringe, using the palpable pulsation under the fingers as a guide. In this case, do not withdraw completely out of the skin, merely pull back and redirect towards the pulsation.
   
10. After 2-3 i-nl of blood has been obtained, withdraw the needle quickly and apply the gauze pad using firm pressure at the site for at least 5 minutes. If the patient has a coagulopathy, 10-15 minutes of firm pressure is required. The goal is to avoid a large hematoma or a possible compartment syndrome. One trick is to use one's elbow to maintain pressure on the gauze pad, leaving the hands free. If the patient is reliable, he/she can be instructed to keep pressure on the pad, or an assistant can hold it.
    
11. Remove any air bubbles from the sample by first removing and disposing of the needle, then hold the syringe upright and tap the syringe to cause any bubbles to rise. Cover the tip of the syringe with a gauze pad to catch any expelled blood. Gently push the plunger to expel all the air bubbles. The gauze catches any expelled blood. Cap the syringe so that it is airtight, and roll it between the hands to mix the contents. Place the capped syringe on ice.
    
12. Note the time of day, patient's current temperature, and the inspired oxygen concentration on the lab slip and make sure the sample gets to the lab quickly.

Complications

• Thrombosis, hematoma, arterial embolism, arterial spasm, arterial insufficiency with tissue loss, infection, hemorrhage, pseudoaneurysm formation and compartment syndrome.

Interpretation of Results (just the very basics)

Normal values:

• pH: 7.35-7.45
• pO2: 80-100 mmHg
  
• pCO2: 35-45 mmHg
  
• SaO2: >95%
• [HCO3-]: 22-28 mmol/L
  
• Base difference (excess/deficit): -3 to +3 mmol/L

Follow-up

• Make sure that at least 5 minutes of firm pressure is kept over the arterial puncture site to prevent hematoma.

Related tests / procedures

• Use pulse oximetry instead of repeated arterial blood gas samples if the only thing being evaluated is oxygenation. Order a standard blood chemistry panel to calculate the anion gap in metabolic acidosis:
  
• Anion gap = [Na+] - ([CI-] + [HCO3-]
  
• Normal range = 8-12 mmol/L